National Operating Committee Research Articles

Instrumented Mouthguard Decoupling Affects Measured Head Kinematic Accuracy

Many recent studies have used boil-and-bite style instrumented mouthguards to measure head kinematics during impact in sports. Instrumented mouthguards promise greater accuracy than their predecessors because of their superior ability to couple directly to the skull. These mouthguards have been validated in the lab and on the field, but little is known about the effects of decoupling during impact. Decoupling can occur for various reasons, such as poor initial fit, wear-and-tear, or excessive impact forces. To understand how decoupling influences measured kinematic error, we fit a boil-and-bite instrumented mouthguard to a 3D-printed dentition mounted to a National Operating Committee on Standards for Athletic Equipment (NOCSAE) headform. We also instrumented the headform with linear accelerometers and angular rate sensors at its center of gravity (CG). We performed a series of pendulum impact tests, varying impactor face and impact direction. We measured linear acceleration and angular velocity, and we calculated angular acceleration from the mouthguard and the headform CG. We created decoupling conditions by varying the gap between the lower jaw and the bottom face of the mouthguard. We tested three gap conditions: 0 mm (control), 1.6 mm, and 4.8 mm. Mouthguard measurements were transformed to the CG and compared to the reference measurements. We found that gap condition, impact duration, and impact direction significantly influenced mouthguard measurement error. Error was higher for larger gaps and in frontal (front and front boss) conditions. Higher errors were also found in padded conditions, but the mouthguards did not collect all rigid impacts due to inherent limitations. We present characteristic decoupling time history curves for each kinematic measurement. Exemplary frequency spectra indicating characteristic decoupling frequencies are also described. Researchers using boil-and-bite instrumented mouthguards should be aware of their limitations when interpreting results and should seek to address decoupling through advanced post-processing techniques when possible.

Development of the NOCSAE Standard to Reduce the Risk of Commotio Cordis.

Commotio cordis, sudden cardiac death (SCD) caused by relatively innocent impact to the chest, is one of the leading causes of SCD in sports. Commercial chest protectors have not been demonstrated to mitigate the risk of these SCDs. To develop a standard to assess chest protectors, 4 phases occurred. A physiological commotio cordis model was utilized to assess variables that predicted for SCD. Next, a surrogate model was developed based on data from the physiological model, and the attenuation in risk was assessed. In the third phase, this model was calibrated and validated. Finally, National Operating Committee on Standards for Athletic Equipment adopted the standard and had an open review process with revision of the standard over 3 years. Of all variables, impact force was the most robust at predicting SCD. Chest wall protectors which could reduce the force of impact to under thresholds were predicted to reduce the risk of SCD. The correlation between the experimental model and the mechanical surrogate ranged from 0.783 with a lacrosse ball at 30 mph to 0.898 with a baseball at 50 mph. The standard was licensed to National Operating Committee on Standards for Athletic Equipment which initially adopted the standard in January 2018, and finalized in July 2021. An effective mechanical surrogate based on physiological data from a well-established model of commotio cordis predicts the reduction in SCD with chest protectors. A greater reduction in force provides a great degree of protection from commotio cordis. This new National Operating Committee on Standards for Athletic Equipment standard for chest protectors should result in a significant reduction in the risk of commotio cordis on the playing field.

Advancing Commotio cordis Safety Standards Using the Total Human Models for Safety (THUMS).

Commotio cordis is one of the leading causes of sudden cardiac death in youth baseball. Currently, there are chest protector regulations regarding the prevention of Commotio cordis in baseball and lacrosse; however, they are not fully optimized. For the advancement of Commotio cordis safety, it is vital to include various age groups and a variety of impact angles in the testing process. This study employed finite element models and simulated Commotio cordis-inducing baseball collisions for different velocities, impact angles, and age groups. Commotio cordis risk response was characterized in terms of left ventricular strain and pressure, chest band and rib deformation, and force from impact. Normalized rib and chest band deformation when correlated with left ventricular strain resulted in R2 = 0.72, and R2 = 0.76, while left ventricular pressure resulted in R2 = 0.77, R2 = 0.68 across all velocities and impact angles in the child models. By contrast, the resultant reaction force risk metric as used by the National Operating Committee on Standards for Athletic Equipment (NOCSAE) demonstrated a correlation of R2 = 0.20 in the child models to ventricular strain, while illustrating a correlation to pressure of R2 = 0.74. When exploring future revisions to Commotio cordis safety requirements, the inclusion of deformation-related risk metrics at the level of the left ventricle should be considered.

Impact attenuation capabilities of new and used football helmets

Football helmets are expected to break down with use, and reconditioning recommendations are required to be stated by manufacturers. However, the degree of change in helmet impact mitigation performance as a function of usage is not generally known. Therefore, this study aimed to compare the ability of football helmets to attenuate impacts after a single season of regular collegiate use to unused helmets. Three never-used Riddell® Speed™ helmets were tested and compared to three used helmets which had been used during one season of Division 1 collegiate football. Helmets were tested at three velocities (3.46, 4.88, and 5.46 m s−1) on six locations in ambient temperature, simulating National Operating Committee on Standards for Athletic Equipment certification drop tests. The interaction between helmet age and location during all three velocities (P 0.0001), indicating that there were differences in Gadd severity index (GSI) between new and used helmets after accounting for location-specific differences. Similar analysis for peak linear acceleration (PLA) found significant interactions for all three velocities (P 0.003). Additional analyses found differences in velocity-dependence for several impact locations. In most cases, used helmets yielded lower GSI and PLA relative to new helmets. The reduction in impact metrics for used helmets indicates initial break-in with impact mitigation benefits, but the long-term consequences of continued use are unclear. The implications of these differences on injury risk and susceptibility remain unknown; however, the results suggest that further studies could inform helmet reconditioning guidelines and development of new smart materials designed to monitor and/or prevent breakdown in padding.

The effect of the head surrogate on the performance of bicycle helmets

Inconsistent results have been reported for helmeted impact responses between the two most commonly used headforms: The National Operating Committee on Standards for Athletic Equipment (NOCSAE) and the Hybrid III (HIII). There is a need to understand the reasons for the different responses of the headforms so that helmet protection may be discerned independent of the headform. In this study, the kinematic response and brain injury measures of the NOCSAE and HIII headforms at three impact orientations with three helmet models on an inclined anvil were compared. The results showed that the peak linear acceleration from the two headforms were within 6.3% on average for all impacts. However, despite the higher moment of inertia of the HIII headform, it did not have a consistently lower rotational acceleration compared to the NOCSAE headform. The differing headform rotational responses were primarily due to differences in the headforms’ center of gravity location. This led to differences in couples and accelerations, which tended to be most severe in frontal impact orientations. The variation in rotational responses of the headforms seems to be also dependent on the helmet type, with helmet A having greater variation compared to helmets B and C. Differences in the rotational kinematics of the two headforms led to a 47% average difference in their brain injury measures.

Addendum.

Swartz EE, Register-Mihalik JK, Broglio SP, et al. National Athletic Trainers' Association Position Statement: Reducing Intentional Head-First Contact Behavior in American Football Players. J Athl Train. 2022;57(2):113–124. doi: https://doi.org/10.4085/1062-6050-0062.21Please see the authors' disclosures below.Erik E. Swartz, PhD, ATC, has received grants from the GOG Hawaii Foundation and the Nine Sigma Head Health Challenge and trademark registration for HUTT. Johna K. Register-Mihalik, PhD, LAT, ATC, has received grants from the National Operating Committee on Standards for Athletic Equipment, Department of Defense (DOD), Centers for Disease Control and Prevention (CDC), National Center for Injury Prevention and Control, National Athletic Trainers' Association (NATA) Foundation, National Football League (NFL), and National Collegiate Athletic Association (NCAA)–DOD Mind Matters Research Challenge Award; she is a member of USA Football's Football Development Council. Steven P. Broglio, PhD, ATC, has received funding from the National Institutes of Health, CDC, DOD-USA Medical Research Acquisition Activity, NCAA, NATA Foundation, NFL, Under Armour/GE, Simbex, and ElmindA. He has consulted for the NCAA (travel expenses only), US Soccer, US Cycling (unpaid), and medicolegal litigation and received speaker honoraria and travel reimbursements for talks given. He is on the University of Calgary SHRed Concussions external advisory board (unpaid). Jason P. Mihalik, PhD, CAT(C), ATC, has received grants from the National Institutes of Health, NFL, CDC, and DOD. Kevin M. Guskiewicz, PhD, ATC, has received grants from the NFL (subaward from Boston Children's Hospital) and NCAA and nonfinancial support from the NCAA Scientific Committee. Julian Bailes, MD, is Chairman of the Medical Advisory Committee for Pop Warner Football. Jay L. Myers, PhD, reported no disclosures. Merrill Hoge, BA, has received royalties from Mascot Books for a football-related publication.

A destructible headform for the assessment of sports impacts

Commercially available headforms, such as the Hybrid-III and EN 960 headforms, have been used effectively to investigate the mechanics of head impacts. These headforms may result in accelerations that are unrepresentative of a human head in some impact scenarios. This may be important when considering impacts that produce areas of high pressure, since skull deformation and resonance excitation may influence the dynamic response. The National Operating Committee on Standards for Athletic Equipment (NOCSAE) headform may produce a more suitable response during these types of impacts due to the more representative skull component. However, permanent deformation may occur in some unprotected impact scenarios, resulting in the entire headform needing to be replaced. This paper outlines the development of a novel, modular and destructible headform (LU headform) that can be used in potentially destructive testing, where individual components can be replaced. The LU headform was modelled after a UK 50th percentile male. The inertial properties of the LU headform were within 6% of those observed in humans. The skull simulant properties were within the range of values reported for human tissue in two build orientations, but lower in one build orientation. The lowest and highest resonance frequencies observed in the headform model were within 5% of those observed in humans. Drop and projectile tests were conducted in line with previous cadaver tests with the observed accelerations within the range reported for post-mortem human subjects. The LU headform offers a practical means of simulating head dynamics during localised unprotected impacts or in protected impacts where local deformation and/or resonance frequency excitation remains possible.

Brain trauma exposure for American tackle football players 5 to 9 and 9 to 14 years of age

American football helmets used by youth players are currently designed and tested to the same standards as professionals. The National Operating Committee on Standard and Safety requested research aiming at understanding the differences in brain trauma in youth American football for players aged five to nine and nine to fourteen years old to inform a youth specific American football standard. Video analysis and laboratory reconstructions of head impacts were undertaken to measure differences in head impact frequency, event types, and magnitudes of maximum principal strain (MPS) for the two age groups. Overall frequencies and frequencies for five categories of MPS representing different magnitudes of risk were tabulated. The MPS categories were very low (<0.08), low (0.08–0.169), medium (0.17–0.259), high (0.26–0.349) and very high (>0.35). Both cohorts experienced a majority of head impacts (>56%) at very low magnitude of MPS. Youth American football players aged 9–14 yrs. sustained a greater frequency of head impacts at MPS between 0.08 and 0.169 % associated with changes in brain structure and function. There were no differences in overall frequency, or in frequency of head impacts in other categories of MPS. The proportion of impacts considered injurious (MPS > 0.08) was greater in the 5–9 group (44%), than the 9–14 group (39%), and impacts above 0.35 % were only reported for the younger age group. The larger helmet-to-shoulder ratio in the younger age groups may have contributed to this finding suggesting that youth American football players under the age of nine would benefit from a child-specific football helmet.

Reduction of High School Ice Hockey Injuries With Implementation of New Checking/Boarding Rules.

Evaluate whether rule changes by the National Federation of State High School Associations (NFHS) were associated with reduced injury rates in US high school ice hockey players. We compared injury rates for the 3 seasons before the rule changes (2011-2012, 2012-2013, and 2013-2014) with the 2 subsequent seasons (2014-2015 and 2015-2016) using data from the High School Reporting Information Online (RIO) database. Convenience sample of US high schools. High school ice hockey athletes. The sports injury surveillance system that supplied the data for this study was funded in part by the Centers for Disease Control and Prevention (grant Nos. R49/CE000674-01, R49/CE001172-01, and R49/CE002106-01) as well as research funding contributions of the NFHS, National Operating Committee on Standards for Athletic Equipment (NOCSAE), DonJoy Orthotics, and EyeBlack. The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention or any other funding agency. In the 2014 to 2015 ice hockey season, the NFHS increased the penalty for boarding (illegally causing opponent to be thrown violently into the boards) and for checking from behind. Injury rates and mechanism of injury. There was a statistically significant 40% reduction in rates of injury attributed to being checked in the 2 seasons after the rule changes (5.0 injuries per 10 000 athlete exposures) compared with the 3 previous seasons (8.3) (rate ratio = 0.60, P = 0.002). There were no significant differences in overall injury rates (P = 0.12) or injury rates due to checking (P = 0.27), contact with the boards (P = 0.31), or contact with another player (P = 0.55). Among US high school ice hockey athletes, implementation of stricter penalties for boarding and checking from behind was associated with a significant decrease in injury rate due to being checked. Rates of injury due to other mechanisms were not significantly altered, suggesting the rule changes achieved their targeted effect.

Relating on-field youth football head impacts to pneumatic ram laboratory testing procedures.

A youth-specific football helmet testing standard has been proposed to address the physical and biomechanical differences between adult and youth football players. This study sought to relate the proposed youth standard-defined laboratory impacts to on-field head impacts collected from youth football players. Head impact data from 112 youth football players (ages 9-14) were collected through the use of helmet-mounted accelerometer arrays. These head impacts were filtered to only include those that resided in corridors near prescribed National Operating Committee on Standards for Athletic Equipment (NOCSAE) impact locations. Peak linear head acceleration and peak rotational head acceleration magnitudes collected from pneumatic ram impactor tests as specified by the proposed NOCSAE youth standard were compared to the distribution of on-field head impacts. All laboratory impact tests were among the top 10% in terms of magnitude for Severity Index and peak rotational acceleration of matched location head impacts experienced by youth football players. As concussive head impacts are among the most severe impacts experienced on the field, a safety standard geared toward mitigating concussion should assess the most severe on-field head impacts. This proposed testing standard may be refined as more becomes known regarding the biomechanics of concussion among youth athletes.

Determinants Of Head Impact Exposure In Youth Football

Concussions are on the minds of many football players, parents and coaches; but attention has increased toward the potentially damaging effects of repetitive, subconcussive head impacts, particularly among youth football players. Advocates of the sport are looking for ways to improve player safety and reduce the potential risk of long-term brain abnormalities. PURPOSE: To identify intrinsic and extrinsic characteristics of play associated with head impact exposure in youth football. METHODS: Head impacts from one youth football team (7th & 8th grade) were measured during every practice and game during the 2018 & 2019 football seasons via a sideline head impact telemetry system and subsequently evaluated using video collected during each session. Each verified head impact was scored using a validated rubric consisting of up to 12 discrete characteristics of play (5 intrinsic, 7 extrinsic). The mean, median and 95th percentile linear acceleration (LA) was calculated for each play characteristic. RESULTS: Over two seasons, 1202 practice (median LA: 19.90 g) and 1571 game (median LA: 21.00 g) head impacts (2773 total) were examined. The “kickoff” (n = 95 impacts; 6% of all game impacts) had the highest 95th percentile LA (69.89 g) among all game play types (e.g., “run”, “pass”, “punt”, etc.). Impacts that occurred “outside the hash marks” (61.75 g) and in the “redzone” (59.40 g) had the highest 95th percentile LA rankings among horizontal and vertical field positions, respectively. When players did not anticipate being hit (n = 53; 1.9% of all impacts), head impacts had a 95th percentile LA of 69.52 g, compared to 47.02 g when they anticipated the impact. Head impacts resulting from players’ helmets hitting the ground (95th percentile LA: 72.94 g) accounted for 11.6% of all impacts (n = 323). CONCLUSIONS: These data indicate that certain, modifiable characteristics of play are associated with higher magnitude head impacts in youth football. Additional research is warranted to continue to examine practice and game situations (extrinsic characteristics) that produce higher magnitude head impacts, which could assist football-governing bodies in developing or modifying policy guidelines to help make the game safer. Supported by a grant from The National Operating Committee on Standards for Athletic Equipment (NOCSAE).

Development and Multi-Scale Validation of a Finite Element Football Helmet Model

Head injury is a growing concern within contact sports, including American football. Computational tools such as finite element (FE) models provide an avenue for researchers to study, and potentially optimize safety tools, such as helmets. The goal of this study was to develop an accurate representative helmet model that could be used in further study of head injury to mitigate the toll of concussions in contact sports. An FE model of a Schutt Air XP Pro football helmet was developed through three major steps: geometry development, material characterization, and model validation. The fully assembled helmet model was fit onto a Hybrid III dummy head–neck model and National Operating Committee on Standards for Athletic Equipment (NOCSAE) head model and validated through a series of 67 representative impacts similar to those experienced by a football player. The kinematic and kinetic response of the model was compared to the response of the physical experiments, which included force, head linear acceleration, head angular velocity, and carriage acceleration. The outputs between the model and the physical tests were quantitatively evaluated using CORelation and Analysis (CORA), amounting to an overall averaged score of 0.76. The model described in this study has been extensively validated and can function as a building block for innovation in player safety.

Comparison of head impact attenuation capabilities between a standard American football helmet and novel protective equipment that couples a helmet and shoulder pads

Concussive and subconcussive sports-related head impacts are common in the United States, particularly in American football. Football helmets are constantly improving upon their predecessors and are proven to reduce head impact kinematics and the risk of sports-related head injury. All football helmets are required to pass certification testing overseen by the National Operating Committee on Standards for Athletic Equipment (NOCSAE) before they are permitted for use. A new advance in protective equipment involves coupling a helmet and shoulder pads as one connected piece of protective equipment. These protective gears cannot be tested using the standard NOCSAE method as they are worn over a user’s head, neck, and upper torso. We aimed to test the effectiveness of a prototype of a coupled, one-piece design, relative to a standard football helmet, using a custom drop tower method of testing. Relative to the standard football helmet, the coupled design reduced measures of peak linear acceleration at front, side, and rear impacts (p < .001) and peak rotational acceleration at all tested head locations (p < .004). The coupled design was also more effective than the standard helmet in attenuating the resultant upper neck force (p < .004) at all tested head impact locations and resultant upper neck moment at rear and side impact locations (p < .048). Future iterations of coupled, one-piece designs should use the results of this study to make improvements to the device, and further investigations on the effectiveness and safety implications of the protective gear are necessary.

Development of a Methodology for Simulating Complex Head Impacts With the Advanced Combat Helmet.

Blunt impact assessment of the Advanced Combat Helmet (ACH) is currently based on the linear head response. The current study presents a methodology for testing the ACH under complex loading that generates linear and rotational head motion. Experiments were performed on a guided, free-fall drop tower using an instrumented National Operating Committee for Standards on Athletic Equipment (NOCSAE) head attached to a Hybrid III (HIII) or EuroSID-2 (ES-2) dummy neck and carriage. Rear and lateral impacts occurred at 3.0 m/s with peak linear accelerations (PLA) and peak rotational accelerations (PRA) measured at the NOCSAE head center-of-gravity. Experimental data served as inputs for the Simulated Injury Monitor (SIMon) computational model to estimate brain strain. Rear ACH impacts had 22% and 7% higher PLA and PRA when using the HIII neck versus the ES-2 neck. Lateral ACH impacts had 33% and 35% lower PLA and PRA when using HIII neck versus the ES-2 neck. Computational results showed that total estimated brain strain increased by 25% and 76% under rear and lateral ACH impacts when using the ES-2 neck. This methodology was developed to simulate complex ACH impacts involving the rotational head motion associated with diffuse brain injuries, including concussion, in military environments.

Influence of ATD versus PMHS reference sensor inputs on computational brain response in frontal impacts to advanced combat helmet (ACH)

ABSTRACTObjective: This study analyzed the influence of reference sensor inputs from anthropomorphic test devices (ATDs) versus postmortem human subjects (PMHSs) on simulations of frontal blunt impacts to the advanced combat helmet (ACH).Methods: A rigid-arm pendulum was used to generate frontal impacts to ACHs mounted on ATDs and PMHS. An appropriately sized ACH was selected according to standard fitting guidelines. The National Operating Committee on Standards for Athletic Equipment (NOCSAE) head was selected for ATD tests due to shape features that enabled a realistic helmet fit. A custom procedure was used to mount a reference sensor internally near the center of gravity (CG) of the PMHS. Reference sensor data from the head CG were used as inputs for the Simulated Injury Monitor (SIMon). Brain responses were assessed with the cumulative strain damage measure set at 10%, or CSDM(10).Results: Compared to ATD tests, PMHS tests produced 18.7% higher peak linear accelerations and 5.2% higher peak angular velocities. Average times to peak for linear accelerations were relatively similar between ATDs (5.5 ms) and PMHSs (5.8 ms). However, times to peak for angular velocities were higher by a factor of up to 3.4 for PMHSs compared to ATDs. Values for were also higher by a factor of up to 13.1 when PMHS inputs were used for SIMon.Conclusions: The preliminary findings of this work indicate that small differences in ATD versus PMHS head kinematics could lead to large differences in strain-derived brain injury metrics such as CSDM.

Event-specific impact test protocol for ice hockey goaltender masks

ABSTRACT Goaltenders in the sport of ice hockey are at high risk for concussions from falls to the ice, player collisions and puck impacts. However, current methods used to certify helmets only consider head accelerations for drop tests which may not describe all common injury mechanisms relating to concussion. The purpose of this study was to describe the characteristics of 3 events associated with concussions for ice hockey goaltenders. A helmeted medium National Operating Committee on Standards for Athletic Equipment (NOCSAE) headform was impacted under conditions representing 3 injury events. Three impact locations’ velocities were selected for each event based on video analysis of real-world concussive events. Peak resultant linear acceleration, rotational acceleration and rotational velocity of the headform were measured. The University College Dublin Brain Trauma Model (UCDBTM) was used to calculate maximum principal strain (MPS) and von Mises stress in the cerebrum. Each impact event produced a unique dynamic response and brain stress and strain values. This demonstrates that a single impact event (i.e. falls) cannot adequately describe all impact events. As a result, impact protocols which assess multiple impact events such as the protocol described in this study should be used to evaluate ice hockey goaltender masks.

Inertial Properties of Football Helmets.

The inertial properties of a helmet play an important role in both athletic performance and head protection. In this study, we measured the inertial properties of 37 football helmets, a National Operating Committee on Standards for Athletic Equipment (NOCSAE) size 7¼ headform, and a 50th percentile male Hybrid III dummy head. The helmet measurements were taken with the helmets placed on the Hybrid III dummy head. The center of gravity and moment of inertia were measured about six axes (x, y, z, xy, yz, and xz), allowing for a complete description of the inertial properties of the head and helmets. Total helmet mass averaged 1834±231 g, split between the shell (1377±200 g) and the facemask (457±101 g). On average, the football helmets weighed 41±5% as much as the Hybrid III dummy head. The center of gravity of the helmeted head was 1.1±3.0 mm anterior and 10.3±1.9 mm superior to the center of gravity of the bare head. The moment of inertia of the helmeted head was approximately 2.2±0.2 times greater than the bare head about all axes.

Comparison of Impact Performance between Youth and Varsity Football Helmets.

Current youth football helmets, intended for players under the age of 14 years old, are similar in design and are tested under the same standard as varsity football helmets. This study evaluated the impact performance of matched youth and adult varsity football helmets. Eight helmet models were evaluated using an impact pendulum, with a modified National Operating Committee on Standards for Athletic Equipment (NOCSAE) medium sized headform mounted on a Hybrid III 50th percentile neck. Four locations on the helmet shell at three impact velocities were tested for three trials, for a total of 576 impact tests. Linear acceleration, rotational acceleration, and a concussion correlate were recorded for each test and a comparison between the youth and varsity helmets were made. It was found that the age group the helmet is intended for did not have a significant effect on the impact performance of the helmet in either linear acceleration, rotational acceleration, or concussion correlate. These results are likely due to the similarities in helmet design resulting from being tested to the same standard. Although it is unknown how a youth helmet should differ from a varsity helmet, differences in impact exposure, anthropometry, physiology, and injury tolerance are factors to consider. These data serves as a reference point for future youth-specific helmet design and helmet standards.

The Ability of an Aftermarket Helmet Add-On Device to Reduce Impact-Force Accelerations During Drop Tests.

The Guardian Cap provides a soft covering intended to mitigate energy transfer to the head during football contact. Yet how well it attenuates impacts remains unknown. To evaluate the changes in the Gadd Severity Index (GSI) and linear acceleration during drop tests on helmeted headforms with or without Guardian Caps. Crossover study. Laboratory. Nine new football helmets sent directly from the manufacturer. We dropped the helmets at 3 velocities on 6 helmet locations (front, side, right front boss, top, rear right boss, and rear) as prescribed by the National Operating Committee on Standards for Athletic Equipment. Helmets were tested with facemasks in place but no Guardian Cap and then retested with the facemasks in place and the Guardian Cap affixed. The GSI scores and linear accelerations measured in g forces. For the GSI, we found a significant interaction among drop location, Guardian Cap presence, and helmet brand at the high velocity (F10,50 = 3.01, P = .005) but not at the low (F3.23,16.15 = 0.84, P = .50) or medium (F10,50 = 1.29, P = .26) velocities. Similarly for linear accelerations, we found a significant interaction among drop location, Guardian Cap presence, and helmet brand at the high velocity (F10,50 = 3.01, P = .002, ω2 = 0.05) but not at the low (F10,50 = 0.49, P = .89, ω2 < 0.01, 1-β = 0.16) or medium (F5.20,26.01 = 2.43, P = .06, ω2 < 0.01, 1-β = 0.68) velocities. The Guardian Cap failed to significantly improve the helmets' ability to mitigate impact forces at most locations. Limited evidence indicates how a reduction in GSI would provide clinically relevant benefits beyond reducing the risk of skull fracture or a similar catastrophic event.

Football helmet impact standards in relation to on-field impacts.

Youth football helmets currently undergo the same impact testing and must satisfy the same criteria as varsity helmets, although youth football players differ from their adult counterparts in anthropometry, physiology, and impact exposure. This study aimed to relate football helmet standards testing to on-field head impact magnitudes for youth and varsity football helmets. Head impact data, filtered to include only impacts to locations in the current National Operating Committee on Standards for Athletic Equipment standard, were collected for 48 collegiate players (ages 18-23 years) and 25 youth players (ages 9-11 years) using helmet-mounted accelerometer arrays. These on-field data were compared to a series of National Operating Committee on Standards for Athletic Equipment standard drop tests with a youth and varsity Riddell Speed helmet. In the on-field data, the adult players had a higher frequency of impact than the youth players, and a significant difference in head acceleration magnitude only existed at the top location (p < 0.001). In the laboratory drop tests, the only significant difference between the youth and varsity helmets was at the 3.46 m/s (61 cm) impact to the front location (p = 0.0421). Drop tests generated head accelerations within the top 10% of measured on-field impacts, at all locations and drop heights, demonstrating that drop tests are representative of the most severe head impacts experienced by youth and adult football players on the field. Current standards have been very effective at eliminating skull fracture and severe brain injury in both populations. This analysis suggests that there is not currently a need for a youth-specific drop test standard. However, there may be such a need if helmet testing standards are updated to address concussion, paired with a better understanding of differences in concussion tolerance between youth and adult populations.